Electric Motor Runs backwards, Cap OK
Electric Motor Runs backwards, Cap OK
(OP)
Hi All,
I have a 110v motor for my home bandsaw that is running backwards. I've researched the issue and looked for what the problem may be. In the process, I purchased and installed a new start capacitor with no change. The motor starts very well but consistently in the wrong direction. If I remove the start capacitor and give the motor a good spin in the correct direction, it runs fine.
I've opened the motor up, and it doesn't appear that it is intended to be reversible. I am able to see the various windings attached to the power leads, but I don't know which wires should be reversed to change the motor direction. Can anyone take a look at the attached picture and let me know which leads should be changed?? Or am i just out of luck?
Motor Pic (2.2mb)
What would have caused the motor to change start direction?
Thanks!
I have a 110v motor for my home bandsaw that is running backwards. I've researched the issue and looked for what the problem may be. In the process, I purchased and installed a new start capacitor with no change. The motor starts very well but consistently in the wrong direction. If I remove the start capacitor and give the motor a good spin in the correct direction, it runs fine.
I've opened the motor up, and it doesn't appear that it is intended to be reversible. I am able to see the various windings attached to the power leads, but I don't know which wires should be reversed to change the motor direction. Can anyone take a look at the attached picture and let me know which leads should be changed?? Or am i just out of luck?
Motor Pic (2.2mb)
What would have caused the motor to change start direction?
Thanks!





RE: Electric Motor Runs backwards, Cap OK
There is a centrifugal switch in your motor that switches the start cap in and out. At rest the switch is supposed to be closed so that when you apply power, the start cap is in the circuit and creates a virtual phase shift in the magnetic field that causes it to spin in the desired direction. Once it gets to speed, the centrifugal switch opens and removes that cap, but the motor is already spinning so it keeps spinning in that direction.
If that switch fails to re-close after the motor is shut down, the start cap, even if good, will not be in the circuit. So then what happens is that the run winding field field is randomly going to spin the motor in either direction. Murphy's Law then takes over to dictate that it will always be the WRONG direction.
If there is no centrifugal switch, then the function is being done by an external device called a "potential relay" that is looking at the back emf of the motor to decide when to switch out the start cap. But he same holds true, it is likely failing open.
"Will work for salami"
RE: Electric Motor Runs backwards, Cap OK
Where would a potential relay typically be located on a motor? I haven't seen any other components, unless the relay is buried somewhere within the windings.
As to your comment on the failure state of the switch, I am certain that it did not fail open, as there is a VERY large difference when you remove the capacitor from the leads. With the capacitor in the circuit, the motor starts easily every time, only running backwards. I have started and stopped the motor at least 100 times and it is consistently always the same direction (Wrong). When I remove the capacitor, the motor does not start at all. I can start the motor in either direction simply by spinning it either way. It will continue running in the direction I spin it.
So to me, this is not an indicator of a switch failing open. In my past experience with the capacitor start compressor, when the switch failed closed, the motor did not achieve full running speed and made a heck of a racket when it was turning. This leads me to think that this is a capacitor run motor with the capacitor wired incorrectly.
As a side thought, is there any way to use a different value capacitor to change the phase and start the motor in a different direction?
Thanks!
RE: Electric Motor Runs backwards, Cap OK
RE: Electric Motor Runs backwards, Cap OK
A little more research, and I think that I can reverse the direction of the motor by flipping the capacitor from wire E to wire C.
I'll give it a try and cage up the capacitor while testing to make sure nothing goes awry.
Thanks!
RE: Electric Motor Runs backwards, Cap OK
RE: Electric Motor Runs backwards, Cap OK
RE: Electric Motor Runs backwards, Cap OK
RE: Electric Motor Runs backwards, Cap OK
RE: Electric Motor Runs backwards, Cap OK
RE: Electric Motor Runs backwards, Cap OK
Thanks!
RE: Electric Motor Runs backwards, Cap OK
Your comment worked perfectly. The motor is back together and running perfectly, in the correct direction :) Thanks for your help!
Thank you to the rest of the posters as well! I appreciate the assistance.
RE: Electric Motor Runs backwards, Cap OK
RE: Electric Motor Runs backwards, Cap OK
RE: Electric Motor Runs backwards, Cap OK